The present invention relates to a hydraulic radial piston machine with steplessly adjustable piston stroke. More particularly, this invention relates to a hydraulic radial piston machine with a rotary cylinder body arranged concentrically to a control pin, and a plurality of pistons which are formed as roller bodies, arranged symmetrically over the periphery of the cylinder and roll on a control curve which is adjustable relative to the cylinder body.
Radial piston machines are known with pistons formed as balls with which only a peripheral line of the ball seals in the cylinder opening and the ball roll over the control curve. It is known in these cylindrical radial piston machines, for changing the piston stroke, to displace the control curve which is generally formed on the inner side of the machine housing about an axis which extends parallel to a rotor of the machine and in direction transverse to the longitudinal direction of the rotor. The control curve can be purely circular curve.
With the use of hydraulic radial piston machines in a hydrostatic drive arrangement for vehicles, a stepless adjustment of the radial piston machine which is formed as a motor is required. Moreover, a compact, space economical construction is desired so as to use such a radial piston machine as a hub motor for the drive wheels of a vehicle. The known radial piston machines with steplessly adjustable piston stroke have the disadvantage in that they have an expensive construction which requires in powerful machines a relatively great space consumption and increases their failure susceptibility. Also, the known radial piston machines in which the pistons are formed as roller bodies and particularly as balls are not suitable for the above-mentioned purposes, since the specific pressure because of the point abutment of the ball-shaped pistons allows with the strength values and respective elasticity coefficients of conventional piston material only a small relative oil pressure independently on the machine dimensions, wherein this oil pressure is very low for the use in the vehicle drive arrangements.